The present invention relates to improvements in cases such as transit containers, and refers more particularly to an improved container fabricated from a flat metal blank and provided with a reinforced corner construction which significantly enhances resistance to fracture of the formed container structure in the corner regions thereof.
Specialized forms of transit cases are used for many purposes. One class of such cases is designed for use in transport and storage of electronic devices, instruments and other materials and devices that easily could be rendered unsuited for intended purposes if housed in inadequate case structures during transportation and handling. By reason of such usage, these cases are designed to be of rugged construction to prevent damage to the case and the devices and goods contained therein. In some applications or usages, these cases must be designed to withstand the testing effects of a free fall and repeated droppings from heights of up to five feet onto a concrete surface. Following the drop testing the cases are inspected to determine if they have retained watertight integrity. If not, they are rejected for use. It is particularly important, therefore, that such cases have high strength character at the corners thereof inasmuch as careless handling, e.g., dropping of the case in use (and which are the conditions duplicated in testing) can result in high shock force transmission to the structure which under such circumstances impacts at the corners more often than at the planar sides. It also is desirable that these cases be of lightweight material construction and that they be fabricated in manners as involves reasonable manufacturing costs.
One method for fabricating cases involves deep drawing an aluminum blank to shape it into a case half which can be used or connected by hinges or otherwise with a like case half to form a case enclosure. While this is a procedure suited to form a structure of, e.g., integral bottom and four side walls, it presents certain disadvantages. For one thing, the drawing operation can produce undesirable varying wall or skin thickness as well as abrasion in the structure reducing the inherent strength thereof. These structures, therefore, do not stand up too well in many drop testing procedures. Also a sharp draw shaping is usually limited to a container wall height of about 10 to 12 inches maximum. Another drawback is that it is more expensive and burdensome to have to perform certain fabrication operations such as punching and shaping the structure walls for reception of appurtenant accessories like hinges, handles etc. than it is to do so on a flat metal blank from which such a case structure can be formed.
In another known method, a case enclosure structure can be formed from a flat metal sheet suitably configured such that by following certain bending steps, the sheet or blank can be erected into a generally rectangularly shaped structure having, e.g., the bottom and four side walls of a case part. In that known method, edges of certain of the wall defining panels of the blank will be welded to others and commonly one wall defining panel will be joined integrally with a perpendicularly disposed adjacent wall defining panel by a convex wall part preferably of parti-hollow cylindrical shape integral with both walls so that there are no sharp dihedral angles where two walls or a wall and the bottom meet. Certain improved case structure characteristics are derived from such arrangement. However, with such case fabrication technique i is not readily possible to form a fully enclosed case corner, i.e., the trihedral defined by the meeting of the three surfaces defined by two adjacent side walls and the bottom. With the described fabrication there is left a small case corner opening which can be, e.g., of T-shape and which must be closed off by filler welding followed by grinding or otherwise dressing that filler material to provide a smooth outside case corner surface. The smoothing or dressing of the curved external surfaces at the corner is a labor intensive procure that it would be advantageous to eliminate. Also, the T-weld is located right at the corner point which is subjected to drop testing and corner impacting in use and is therefore the location where fracture, e.g., separation of container parent material from the weld material, can occur.
Patents which disclose various forms of case corner opening closure and corner reinforcement include U.S. Pat. No. 2,006,673 which discloses use of companion inner and outer metallic corner pieces which sandwich the canvas and waterproof fabric materials of an ice carrier therebetween, the assembly being secured with rivets. U.S. Pat. No. 2,980,285 discloses using a corner block with three arms projecting therefrom and intended to be slid into specially shaped edge rails which receive and hold the case side wall panels. U.S. Pat. No. 2,849,142 relates to a wooden box construction in which longitudinal and transverse strips of wood are secured in notches in the case corner wall junctures, the portions of the strips which project beyond the corner being thereafter removed, e.g., by sanding or the like to provide a smoothly rounded corner surface. U.S. Pat. No. 3,553,823 provides a transport container with special corner pieces comprised of interfitting crossing channel pieces which are welded together and then welded to the three container frame bars which meet at each trihedral-shaped corner of the container. U.S. Pat. No. 4,023,726 discloses a metal container construction in which a spherical corner closure cap is welded to the container wall structure adjacent a corner of the container to cover a corner opening. The closure cap is fitted at the inside of the container, the walls and cap being of companion fitting stepped arrangement so that the cap can more readily resist internal pressure within the container, an arrangement which deals with resistance to forces directly opposite to what is encountered when a container is impacted on the outside of the corner and wherein impact forces would tend to push such cap inwardly of the container.
It is therefore desirable that an improved blank erected container having a more effective corner closure be provided and that it be done so in a way as significantly increases the strength of the corner structure of such cases to resist impact forces which tend to dislodge the cap member inwardly into the container interior. As an adjunct, the corner closure should be such as to materially reduce the fabrication costs by eliminating the welded closure of the corner opening heretofore used.